Today, radiation therapy has a significant place in the treatment of cancer. In recent years, new radiotherapy methods of treatment have begun to be introduced, which, for example, make it possible to control tumors directly during the irradiation process, shortening the procedure time and minimizing the negative impact on the patient. An example of combining diagnostics and radiation therapy is the "Tomotherapy" device, with the help of which a beam of ionizing radiation is directed to the tumor with high accuracy, the built-in computer form determines the size and position of the tumor in a matter of seconds before the start of the session. We propose a method for assessing the distribution of doses in the body during irradiation with medical electron accelerators. The method uses positron emission tomography based on the registration of annihilation photons. It is based on the use of the electron-positron pair production mechanism. The positrons formed in the course of irradiation with photons undergo ionization deceleration and then annihilation with the formation of two photons with an energy of 0.511 MeV. By registering such photons for coincidence, it is possible to obtain the distribution of annihilation events in the irradiated tissue region. In the work, a mathematical model has been created that allows one to estimate the absorbed dose in a given tissue site. Within the framework of the computer experiment performed using the GEANT4 package, the correlation between the distribution of the absorbed dose of the primary photon flux and the distribution of the annihilation density of secondary positrons was estimated. The depth distributions of the absorbed dose and the number of annihilations are obtained, and an empirical recalculation function from the distribution of the number of annihilations in the depth estimate of the absorbed dose is selected.
Show AbstractAn approach to the optimization of the procedure for solving the equations of motion of particles of a discrete self-consistent model of a rarefied plasma based on the conjugation of dynamic schemes of different nature and computational properties is developed. The concept was algorithmically implemented and tested in mathematical modeling (using the PIC method) of the low-frequency kinetic Weibel instability. A significant reduction in the simulation time is shown when using the specified optimization technique in comparison with traditional computation based on only one (explicit or implicit) dynamic scheme. During computer experiments, the features of the behavior of the Weibel process at the stage of its saturation were revealed: the presence of damped low-frequency oscillations of the energy density of the magnetic field, the key parameter of instability.
Show AbstractIn this article, we present the result of a numerical experiment on the acceleration of charged particles in a turbulent field with different levels of intermittency. Our main task was to investigate the effect of intermittency on particle acceleration in turbulent cosmic plasma. For this, a three-dimensional model of a turbulent field with a controlled intermittency level was developed. An intermittent electromagnetic field is modeled as a superposition of a turbulent electromagnetic field with a power-law spectrum, obtained using the sum of the Fourier harmonics and the electromagnetic field created by small plasmoids, the amplitudes of which are specified using a special distribution. Using this model, the role of intermittency in the acceleration of charged particles in a turbulent field in the tail of the magnetosphere was investigated. It is shown that the higher the level of intermittency, the higher the energy values are able to reach individual particles.
Show AbstractIn the paper it is investigated the process of formation of the modern dynamic theory liquid. The activity of N.N.Bogoliubov on the creation of a dynamic theory in statistical physics and the influence of his work on the formation of a dynamic theory of liquid are presented.
Show AbstractThe principles of construction of the framework for General physics webinars are described. The experience of its realization using Discord application and Google Workshop utiltites is discussed.
Show AbstractThe experience of e-learning methods usage for intgrated development of student competences had analyzed. As a teaching method students' specific activity within the General physics laboratory course had proposed: the laboratory activities considered as scientific research. The results of distance education methods usage had described, some significant advantages have found.
Show AbstractThe authors draw attention to the fact that the description of the mechanism of the rainbow and halo formation is absent in both school and university textbooks and teaching aids. An explanation of these phenomena is given in the popular science literature, but there is no indication of the fact of the polarization of the rainbow and the reasons for this polarization. At the same time, these phenomena can be studied within the framework of a general course in physics, spending about half an hour in seminars. The article provides a methodology for studying rainbows and halos with students. In addition, the authors draw attention to a common mistake associated with the history of Descartes' study of the rainbow.
Show AbstractThe experience of teaching the courses "General issues of methods of teaching physics and mathematics in higher education" for master's students and "Fundamentals of teaching physics in higher education" for postgraduate students in a distance format at the Faculty of Physics of Moscow State University in the autumn semester of the academic year 2020-2021 is discussed. In the context of the coronavirus pandemic, these courses, like other lecture courses taught at the Faculty of Physics, had to be transferred to a remote format. As a result, in order to maintain interest in the courses and not lose feedback from the listeners, the principles of working with students and postgraduates were reworked. This paper discusses new approaches to working with students and postgraduates, provides examples of tasks that were offered to be performed in a remote format.
Show AbstractThe equations of state are investigated for a system of hard spheres in the general quantum-mechanical case. The equations are presented in the reduced form. A comparison is made between the classical approximation, the semiclassical approximation with allowance for the first correction, and the cell-cluster expansion with allowance for three-particle clusters, inclusive. The cell-cluster expansion, as calculations show, is more efficient than the semiclassical approximation at high densities. It is shown that the density dependence in the caloric equation of state is significant, which is also preserved at high temperatures. In the general case, Joule's law does not hold for a system of hard spheres.
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